1. Field of the Invention
The present invention relates generally to a system for detecting cylinder pressure in internal combustion engines for automotive vehicles. More specifically, the invention relates to a cylinder pressure detecting system which can decrease variation of cylinder pressure detection values in respective cylinders.
2. Description of The Background Art
In order to diagnose or detect combustion conditions in an internal combustion engine, cylinder pressure is generally detected by means of a cylinder pressure detecting system. Such detection systems have been disclosed in Japanese Patent Second (examined) Publication (Tokko Sho.) No. 41-5154, SAE Technical Paper No. 750883 and so forth. The disclosed systems are designed to detect cylinder pressure on the basis of an output of a ring-shaped pressure sensor which is sandwiched between mounting surfaces of an ignition plug which engages a cylinder head.
On the basis of the detected cylinder pressures in respective cylinders, a misfire is determined for individual cylinders. In addition, mean effective pressures Pi for respective cylinders are calculated on the basis of the respective cylinder pressures. On the basis of surge torque detected from fluctuation of the mean effective pressures Pi, inadequate settings for ignition timing and EGR (exhaust gas recirculation) for respective cylinders are corrected. Furthermore, on the basis of the mean effective pressures Pi, fuel injection amounts for respective cylinders are corrected so as to decrease variation of air/fuel ratios for respective cylinders.
However, variations in output characteristics are often produced in pressure sensors used for cylinder pressure detecting systems when they are manufactured. In addition, variation may be caused due to incorrect clamping torque when the pressure sensor is sandwiched between the mounting eye surfaces of the ignition plug for mounting therebetween. As a result, variation in output level of the pressure sensor is often produced.
For these reasons, the absolute value of the cylinder pressure detected by pressure sensor can not be accurately measured. Therefore, there is a disadvantage in that it is difficult to obtain predetermined accuracy in a case where determination of misfire, surge torque control, fuel injection modification control and so forth must be performed using a cylinder pressure detecting system of the aforementioned type.